A powerful earthquake and several aftershocks have struck off the western Indonesian island of Sumatra, sparking fears of a tsunami.

Tsunami alerts were issued for several nations in the Indian Ocean, though some have now been lifted.

Buildings collapsed on the west coast of Sumatra. Hospitals are on alert in case there are significant casualties.

A massive undersea earthquake sparked a tsunami that killed more than 220,000 people in December 2004.

The Pacific Tsunami Warning Centre issued an alert for the entire Indian Ocean region following Wednesday's main quake, which the US Geological Survey said measured 8.4.

Danger eases

Besides Indonesia, India, Sri Lanka, Malaysia and a number of small islands were put on alert. Kenya, on the western rim of the ocean, also raised the alarm.

There were unconfirmed reports of a small tsunami - estimated at 1-3m (3-10ft) hitting the Sumatran coast - but not causing major damage.

But about two hours after the quake, Indonesia's meteorology agency said the danger of a serious tsunami had passed, and Sri Lanka and India also dropped their alerts.

Wednesday's main earthquake struck at 1810 (1110 GMT), about 30km (18 miles) under the sea, some 130km (80 miles) south-west of the city of Bengkulu, the US Geological Survey said.

Local media said buildings had collapsed in Padang, the capital of the province of West Sumatra, and in the town of Mukomuko.

There were also reports of inhabitants fleeing swaying buildings in the capital Jakarta, 600km (370 miles) away, and in Singapore.

"You could see the road as if it was waving, people could hardly walk so they just lay flat on the road. I could also feel the earth I was standing on was like the sea," Zulkifli Lubis, a local journalist in Bengkulu, told the BBC.

Damage

Officials said it was very difficult to get clear communications with the area to make damage assessments.